Two-way Valve

The two-way valve limits the pressure and depression in the fuel tank and, during refuelling, induces automatic cut-off in the refuelling nozzle when the fuel in the tank reaches the full level. The two-way valve is installed in the vent pipe from the tank, next to the fuel pump assembly.

The two-way valve is a normally closed valve that opens, to release pressure from the fuel tank, at 18 to 50 mbar (0.26 and 0.73 lbf/in² ). Air is allowed to flow back into the fuel tank, as the pressure in the tank decreases, through a non return valve within the body of the two-way valve. The nominal opening pressure of the non return valve is 1 mbar (0.015 lbf/in² ).

During refuelling, if the fuel in the tank reaches the full level outward venting becomes restricted, which creates a back pressure in the filler tube and automatically closes the refuelling nozzle. On all except NAS vehicles, the restriction is caused by the fuel covering the outlet to the vent pipe connected to the top of the filler tube. On NAS vehicles, the restriction is caused by the fuel closing the ORVR valve.